Colorant-containing polymer particles consisting of a complex of a resin (polymer) and a colorant are used as electrophotographic toner particles and immunological diagnostic reagent carriers.
It is preferable that colorant-containing polymer particles used for these applications be as small in particle size as possible; there is a need for the development of colorant-containing polymer particles having a small particle size of about 0.5 .mu.m.
In the field of electrophotographic toners, for instance, toner particle size and shape can easily be controlled, if toner particles are prepared by associating colorant-containing polymer particles of small particle size. The toner particles thus obtained are expected to be smaller in particle size and narrower in particle size distribution than toner particles prepared by so-called the kneading milling method or the like.
In the field of immunological diagnostic reagent carriers, particle size reduction for colorant-containing polymer particles is expected to provide immunological diagnostic reagents of high coagulation speed and high sensitivity.
With these aspects in mind, the present inventors investigated particle size reduction for polymer particles containing pigment particles as a colorant.
In producing pigment-containing polymer particles using inorganic pigment particle, for instance, the following technologies can be applied.
1) Encapsulation polymerization of inorganic pigment on the basis of lower critical consolute temperature [Journal of American Chemical Society, 200, 131 (1984]. PA1 2) Encapsulation polymerization of inorganic pigment by emulsification polymerization [journal of Polymer Science: Part A: Polymer Chemistry, Vol. 25, 3117-3125 (1987].
However, complexation of inorganic pigment particles (inorganic substance) and a polymer (organic substance) is difficult due to a lack of hydrophilicity on their surfaces and due to the polymerization stopping action of some inorganic pigment particles. When inorganic pigment particles of small particle size, in particular, are used, comptexation of said inorganic pigment particles and the polymer is very difficult.
Also, with respect to polymer particles containing an organic pigment, particle size reduction is very difficult.